Molecular basis of inheritance Flashcards
what gave the most conclusive evidence about DNA being the genetic material?
The Hershey and Chase experiment in bacteriophages
What is the Griffith’s experiment?
This is an experiment in which Griffith proves that DNA is the genetic material and not the proteins. S straina and R strain.
What is transformation?
The phenomenon by which DNA when isolated from cell is introduced into the other , it bestows some of its properties to the other cell.
What is the Avery,McCleod and McCarry’s experiment?
In this experiment three scientists performed these experiments in-vitro and after transferring the genetic material of the S cell to the R cell, he realised that the R cell transformed into the S cell. He treated the extract with DNAase which prevented the transfer of species , he also treated it with proteases and found that nothing happened.
What was the Hersheys and Chase exp. ?
It was the exp. that dealt with the T2 Bacteriophage.
Why was the T2 Bacteriophage used?
It was used because it contained only two things, a protein head and genetic material inside.
What were the two virus strains created for the experiment.
Since sulphur was not found in DNA, proteins were labelled with radioactive sulphur and DNA with radioactive phosphorus.
What properties must a molecule have in order to act as genetic material?
- Replication
- Chemically and structurally stable
- expression in the form of mendelian characters
- It should be able to mutate
Which molecules are the foundation of life?
Nucleic acids
What are nucleic acids?
They are large polymeric molecules composed of repeating units called nucleotides
What is a nucleotide composed of ?
- Nitrogenous base
- Pentose sugar
- Phosphate
Where does DNA occur?
- Chromosomes
- Plastids
- Mitochondria
Where does RNA occur?
- Chromosomes
- Nucleoli
- Cytoplasm
- Ribosomes
- Plastids
- Mitochondria
What is Chargaff’s rule?
This rule states that the ratio of purines to pyrimidines is one. i.e. , the no. of A is equal to the no. of T etc.
What did Franklin and Wilson notice about the structure of DNA?
- Helical
- Diameter 20Å
- The distance between successive nucleotides 3.4Å
- This helix makes one complete turn every 34Å
- There are ten nucleotides per turn
What did Watson and Crick propose?
They proposed the double helix model of DNA
What should you mention describing the structure of DNA?
- Its dimensions given by Wilkin and Franklin
- Double stranded(fulfilling density requirements)
- Hydrogen bond
- Sugar-Phosphate alternate backbone
- Antiparallel
- Complementary
What are the different types of RNA?
- Ribosomal RNA
- Messenger RNA
- Transfer RNA
In which ways do these types of RNA vary ?
In size and function.
Which is the largest RNA?
rRNA
Where is mRNA produced?
The nucleus
Just a note:
mRNA is specific for each protein
Which is the most abundant RNA?
Ribosomal
Which is the stable form of RNA?
Ribosomal
Which RNA has the highest molecular weight?
Ribosomal
What helps in the binding of the mRNA and tRNA?
The rRNA molecule helps in the of mRNA and tRNA to the ribosome. This bond occurs using a Mg2+ linkage btw the phosphate molecules of the two RNAs.
Which RNA is the most heterogenous is size and stability?
mRNA
Where does mRNA occur?
It occurs in the nucleolar region and the cytoplasm
IMP things about an mRNA molecule.
- Its size varies depending on the protein it codes for
- It carries coded message from a DNA molecule to a Ribosome and instructs the amino acids to sequence in protein synthesis
- mRNA is short lived
- Hence it does not accumulate in cells
The matching of anticodon with amino acid is done by…?
Amino acyl- tRNA synthetase
What method did Watson and Crick propose for the replication of DNA?
They proposed the semiconservative method of replication.
What was the Meselson- Stahl experiment?
E.coli cultures with heavy and light Nitrogen isotopes.
In the Meselson- Stahl experiment how were the DNA strands analysed?
They used a CsCl density gradient centrifugation technique.
Which enzymes are used in DNA replication?
- Primases
- Helicases
- Topoisomerases
- DNA polymerases
- DNA ligases
- Repair enzymes
What is the origin of replication?
It is the initiation site at which replication occurs
What are replicons?
LInearly arranged units that undergo replication.
What is a primer?
The primer is a short stretch of RNA formed on DNA.
What does the primase enzyme do?
This enzyme polymerises A U G C into the primer.
What is the sense strand?
It is the DNA strand which serves as a template for W
What principle governs the process of transcription?
The principle of complementarity
Why does only strand code take part in transcription.
- This is because if both strands of DNA coded for proteins they would be coding for different proteins. Which would complicate the process.
- The two RNA strands formed would be complementary to each other and form a double stranded DNA
What purposes do deoxyribose triphosphates serve in DNA replication?
They have a dual function, i.e.They act as substrates for reactions and also provide energy for polymerisation reactions. (High energy phosphates)
The term genetic code was coined by whom?
The term genetic code was coined by George Gamow
What is the transcriptional unit?
the transcriptional unit is a structure that consists of
- the promotor
- The structural gene
- A terminator
What is the template strand?
The strand whose polarity is 3’ to 5’ and that strand which acts as the template strand.
What is the template strand also called?
The template strand is also called the non coding strand.
What is the coding strand
This is the strand with the desired code for the RNA. It is also called the sense strand or non- template strand.
Which provides for the binding site of RNA polymerase?
The promoter contains a DNA sequence that does so.
AN IMP NOTE:
It is the position of the promoter strand that determines the coding and template strands.
Certain short sequences of the promoter that are conserved are called…?
Recognition sequence
What does the Terminator do?
It defines the end of a process
What is the functional unit of inheritance
gene
What is a cistron?
This is functional unit of a gene. It is a segment of DNA that codes for a polypeptide.
The structural gene in prokaryotes is usually….. and in eukaryotes is usually …… ?
polycistronic
monocistronic
What are exons?
These are the coding sequences present in a mature or processed RNA.
What are introns?
Exons are interrupted by introns which are intervening sequences that do not appear in mature/sequenced RNA.
Just a note:
This structure of a DNA is called the split gene arrangement.
Where do transcription and translation occur?
In eukaryotes Transcription occurs the nucleus and translation in the cytoplasm.
In which way does the sigma factor help in transcription?
It gives specificity to the initiation process. Without it , initiation could’ve started anywhere.
What is hnRNA synthesised by?
RNA Polymerase II
What are the processes involved in post transcriptional processing?
- 5’ capping
* Tailing and Splicing
What happens in 5’ capping?
Methyl guanosine triphosphate is added to the 5’ end of an hnRNA. This is catalysed by guanylyl transferase. The cap is necessary for the formation of the mRNA ribosome complex.
What is tailing?
It is the addition of 200-300 adenylate residues to the 3’ end in a template independent manner with the help of Poly A Polymerase
What is splicing?
It is the process of removal of introns. It is done by SnRNA and SnRNPs.
What does splicing represent?
It represents the dominance of the RNA world.
How are the the protein and DNA arrange in a bacterial cell.
They are collinear
What are the 5 histone proteins?
H1,H2A,H2B,H3,H4
what is the nucleosome?
It is he combination of an acidic DNA molecule and a basic histone protein
just a note:
200 bp are involved in wrapping around the histone octamer by 7/4 turns
What are the dimensions of a nucleosome?
110 x 60 angstrom
What is the DNA present in btw to nucleosomes
This is the linker DNA
What causes the beads on string appearance?
nucleosomes which coils to form a solenoid
What is the definition of a codon?
A sequence of three nucleotides which together form a unit of genetic code in a DNA or RNA molecule.
What is the genetic code?
The order of base pairs along a DNA molecule controls the kind and order of aas found in the protein of an organism.
